The present invention relates to a hand lever device for manipulating, through a cable, a driven member (a member to be driven) such as a carburetor throttle valve for an internal combustion engine and, in particular, to a hand lever device which is suited for use in a working machine such as a hedge trimmer, bush cutter, etc., and is adapted to be attached close to the grip portion of the handle of the working machine for opening or closing, through a throttle cable, the carburetor throttle valve.
In the case of a working machine such as a hedge trimmer, bush cutter, etc. where a working member thereof such as a cutting blade is arranged to be driven by means of an internal combustion engine, a hand lever for adjusting the opening degree of carburetor throttle valve of the internal combustion engine is usually disposed close to the grip portion of a U-shaped handle or a bar handle of the working machine so as to allow the output of the internal combustion engine to be controlled at hand.
The hand lever device is usually provided with a throttle trigger (throttle lever) that can be manipulated by an operator's finger, thereby enabling the operator to adjust, through a throttle cable, the opening degree of the carburetor throttle valve by pivotally moving the throttle lever. The carburetor throttle valve is generally urged in a direction such as to always set a minimum opening degree at which the carburetor throttle valve is always kept to an opening degree for an idling speed of the engine when the working member is not in an operating state. However, when the throttle cable is pulled to an extent exceeding a predetermined amount beyond the play thereof, the carburetor throttle valve is caused to further open, starting from the idling opening degree toward a setting for a higher engine speed greater than the idling speed.
There are known two types of hand lever devices for adjusting the opening degree of the carburetor throttle valve; i.e., an idling opening degree-automatic reset type (automatic reset type) wherein the hand lever is enabled automatically to return together with the carburetor throttle valve to the original position (idling opening degree) as soon as the throttle lever is released from a position held by the operator's finger and a retention type wherein the throttle lever can be always kept in a stationary state at any desired angle position once the throttle lever is pivotally moved to the desired angle even if the operator releases the throttle lever (Japanese Utility Model Publication S57-19944).
It is possible, according to the aforementioned automatic reset type hand lever, to allow an internal combustion engine to automatically return to an idling engine speed as soon as the throttle lever is released from the operator's finger, thereby cutting off a centrifugal clutch and hence suspending the power transmission of the engine to the working member if the working machine is arranged such that the power transmission of engine to the working member (such as a cutting blade) is to be effected through the centrifugal clutch. Therefore, it is possible, according to the aforementioned automatic reset type hand lever, to immediately cause the carburetor throttle valve to return to the idling opening degree so as to suspend the operation of the working member as soon as any unexpected situation is encountered, thereby advantageously improving the safety of operation. The automatic reset type hand lever is, however, accompanied by the problem that if the carburetor throttle valve is to be maintained at any desired opening degree, the throttle lever has to be always held by the operator's finger in order to maintain the rotated position of the throttle lever, thereby making it inconvenient to manipulate the throttle lever at an intermediate opening degree, causing the operator's finger to become fatigued, and making it difficult for the operator to avoid fluctuation of the position of the lever and thus variation of the engine speed.
As far as the manipulability of the working machine is concerned, it is generally preferable that a manipulating lever to be rotationally manipulated with an operator's finger be arranged to take only two rotational positions, i.e., a released position and a set position (gripped position) without enabling the manipulating lever to take an intermediate opening position. Namely, it is preferable in terms of manipulability to arrange the throttle lever so that it takes the same manipulated rotational position (the set position), irrespective of the opening degree of the carburetor throttle valve, i.e., either an intermediate opening degree (a partial opening degree) or a full opening degree (WOT).
On the other hand, in the case of the aforementioned retention type, it is possible to overcome the aforementioned problems of the automatic reset type hand lever, thus enabling the throttle lever to be always kept in a stationary state at any desired angle position even if the throttle lever is released free from the operator's finger. As a result, the operator's finger can be rendered free from the gripping of the throttle lever, thus facilitating the operation of the working machine. However, it is required, if any unexpected situation is generated, to take an additional manipulation to release the throttle lever position-retaining function, so that it is impossible to immediately suspend the operation of the working member. Namely, the aforementioned retention type is accompanied with a problem that it is inferior in terms of the safety of operation as compared with the aforementioned automatic reset type hand lever.
If it is required, in order to restore the working mode of the machine in either the automatic reset type or the retention type, to return the throttle valve to the previous opening degree of the throttle valve after the throttle lever has been once returned to the initial idling position for interrupting the working (that kind of manipulation is frequently experienced in the case of a working machine such as a bush cutter), the manipulating rotational position of the throttle lever is required to be readjusted, which involves a troublesome manipulation of the throttle lever, thus leaving room for improvement in terms of manipulability of the working machine.
With a view to overcome these problems involved in the aforementioned hand lever devices, the present assignee has already proposed a hand lever device, as set forth in Japanese Patent Unexamined Publication H8-303262, wherein the hand lever device comprises a main lever and a sub-lever which are enabled to pivot and arranged such that the sub-lever functions to pull a cable connected with a driven member via a returning member such as a running block, and the main lever functions to move the returning member.
With such a hand lever device, various advantages can be obtained. For example, the opening degree of the driven member such as a carburetor throttle valve can be easily adjusted and maintained to a desired opening degree via the cable, and also can be quickly returned to the minimum opening degree (idling opening degree), thus assuring a high operational safety and minimizing the weariness of the operator's finger. Additionally, it is possible to dispense with the readjustment of the throttle lever at the time of returning the carburetor throttle valve to the previous opening degree.
However, the hand lever device as proposed previously by the present assignee is still accompanied with the following problems in terms of manipulability.
Namely, the hand lever device cannot be said to be excellent in its ability to restore the previous engine speed when the main lever is pivotally moved to a pre-set position in order to cause the throttle valve to return to the previous intermediate opening degree, after a carburetor throttle valve has been once returned to the idling opening degree by releasing the main lever during the operation of a working machine such as a bush-cutting operation with the engine being conditioned to a partial engine speed region, i.e., the main lever being moved to the set position and the sub-lever being maintained at an intermediate opening degree (adjusted opening degree). In other words, it takes a relatively long time to regain the previous engine speed once the main lever is returned to the idling opening degree as mentioned above.
Further, when the cutting blade of a bush cutter becomes entangled with a weed or is called upon to cut dense or thick weeds during the operation of a bush cutter with the engine speed thereof adjusted to a partial engine speed region, the load on the engine would be greatly increased, thereby greatly decreasing the engine speed and thus retarding the cutting work. In such a case, in order to remove a tangled weed from the cutting blade or to allow the cutting blade to pass through dense or thick weeds, the sub-lever may be further pivotally moved to enlarge the opening degree of the throttle valve so as to temporarily increase the engine speed, after which the sub-lever is returned to the previous opening degree. However, since the sub-lever is generally disposed forwardly relative to the main lever (the grip portion for grasping the main lever) so as to allow the sub-lever to be manipulated with the operator's thumb and since the sub-lever is arranged to be retained at a pivoted position, it is not only troublesome to frequently adjust the opening degree thereof, but also annoying in taking time for adjusting the opening degree thereof, thus making the hand lever device disadvantageous in terms of operability. Therefore, there is a need to develop measures which enable the engine speed to be quickly increased with a simple manipulation when the engine speed is caused to decrease as described above.